The present invention relates to a process for forming tubular components and to products produced by the process.
For the mass-production of tubular components, for example structural tubular components used in the construction of a motor vehicle body, it is desirable to reproduce individual components within reproducible close tolerances whilst maintaining the cost of manufacture as low as possible. As a structural component, it is necessary that the component be manufactured so as to be capable of withstanding working loads in order to provide the desired amount of structural support. It is important therefore that the production process does not introduce undesirable weaknesses into the finished tubular component.
Typically a structural tubular component as used in the construction of a motor vehicle body will be generally elongate and will have length portions which vary in cross-sectional shape and/or size.
Some of these types of components can be formed from a precursor tube of constant cross-sectional shape and size along its length, the precursor tube being worked upon by forming processes such as hydroforming in order to change the shape and size of the precursor tube at predetermined locations along its length.
The forming process may involve several separate forming stages before the final component is produced. Each forming stage adds cost to the overall cost of producing the component and also slows down the overall process. It is also possible that each forming stage introduces weaknesses into the formed material.
It is known for example that when using hydroforming techniques, particularly at low temperatures, the amount by which the tubular component can be expanded is relatively restricted and so if the final component includes length sections of relative large differences in cross-sectional dimension, it is known to produce the precursor tube from separate relative small and large tubular sections which are joined together prior to the forming process.
A general aim of the present invention is to provide a relatively simple process for the expansion of a precursor tube so as to provide a formed tube having integrally joined longitudinal sections of relatively small and large cross-sectional dimensions, the formed tube defining an intermediate precursor tube for subsequent forming processes or defining the finished tubular component.
According to one aspect of the present invention there is provided a process of producing from an elongate tube a tubular structural component having a first longitudinal section integrally collected to a second longitudinal section, the second section being located at the end of the tube and being of a desired cross-sectional shape and size, the cross-sectional size of the second section being greater than that of the first section, the process including selecting a mandrel having a cross-sectional shape and size corresponding to the second sections relatively axially feeding said end of the tube over the mandrel in order to form said second section, the choice of the size of mandrel and the rate of feed and the axial pressure applied to said tube being controlled such that the wall thickness of the second section is on average at least 70 percent of the average wall thickness of the first wall section.
According to another aspect of the present invention there is provided a structural component having been formed at least in part by the process defined above.